num = input()
if len(num) == 4:
  n1 = num[0]
  n2 = num[1]
  n3 = num[2]
  n4 = num[3]
  sp = [int(n1),int(n2),int(n3),int(n4),int(n1 + n2),int(n1 + n2 + n3),int(n1 + n2+ n3 + n4),int(n2 + n3),int(n2 + n3 + n4),int(n3 + n4)]
  sp.sort(reverse = 1)
  for x in sp:
    f =1
    for d in range(2,x //2 + 1):
      if x % d ==0:
       f = 0 
       break
    if f == 1:
     print(x)
     break
  if f == 0:
   print(0)
else:
 print(0)
